ATX Specification

ATX Specification Version 2.1 ATX Specification - Version 2.1 Page 2 IMPORTANT INFORMATION AND DISCLAIMERS 1. INTEL CORPORATION MAKES NO WARRANTIES WITH REGARD TO THIS ATX SPECIFICATION (“SPECIFICATION”), AND IN PARTICULAR DOES NOT WARRANT OR REPRESENT THAT THIS SPECIFICATION OR ANY PRODUCTS MADE IN CONFORMANCE WITH IT WILL WORK IN THE INTENDED MANNER. NOR DOES INTEL ASSUME RESPONSIBILITY FOR ANY ERRORS THAT THE SPECIFICATION MAY CONTAIN OR HAVE ANY LIABILITIES OR OBLIGATIONS FOR DAMAGES INCLUDING, BUT NOT LIMITED TO, SPECIAL, INCIDENTAL, INDIRECT, PUNITIVE, OR CONSEQUENTIAL DAMAGES WHETHER ARISING FROM OR IN CONNECTION WITH THE USE OF THIS SPECIFICATION IN ANY WAY. 2. NO REPRESENTATIONS OR WARRANTIES ARE MADE THAT ANY PRODUCT BASED IN WHOLE OR IN PART ON THE ABOVE SPECIFICATION WILL BE FREE FROM DEFECTS OR SAFE FOR USE FOR ITS INTENDED PURPOSE. ANY PERSON MAKING, USING OR SELLING SUCH PRODUCT DOES SO AT HIS OR HER OWN RISK. 3. THE USER OF THIS SPECIFICATION HEREBY EXPRESSLY ACKNOWLEDGES THAT THE SPECIFICATION IS PROVIDED AS IS, AND THAT INTEL CORPORATION MAKES NO REPRESENTATIONS, EXTENDS NO WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, ORAL OR WRITTEN, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR WARRANTY OR REPRESENTATION THAT THE SPECIFICATION OR ANY PRODUCT OR TECHNOLOGY UTILIZING THE SPECIFICATION OR ANY SUBSET OF THE SPECIFICATION WILL BE FREE FROM ANY CLAIMS OF INFRINGEMENT OF ANY INTELLECTUAL PROPERTY, INCLUDING PATENTS, COPYRIGHT AND TRADE SECRETS NOR DOES INTEL ASSUME ANY OTHER RESPONSIBILITIES WHATSOEVER WITH RESPECT TO THE SPECIFICATION OR SUCH PRODUCTS. 4. A SOFTWARE LICENSE IS HEREBY GRANTED TO REPRODUCE THIS SPECIFICATION FOR ANY PURPOSE PROVIDED THIS “IMPORTANT INFORMATION AND DISCLAIMERS” SECTION (PARAGRAPHS 1-4) IS PROVIDED IN WHOLE. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY OTHER INTELLECTUAL PROPERTY RIGHTS IS GRANTED HEREIN. Copyright  1996, 1997, 1998, 2002 Intel Corporation. All rights reserved. Version 2.1, June 2002 † Third-party brands and names are the property of their respective owners. ATX Specification - Version 2.1 Page 3 Revision History Changes from Version 2.03 to Version 2.1 Global change—Removed references to Mini-ATX Section 2—Replace existing text with new text that adds requirement for ATX12V connector; substitute revised Figure 1 Section 3.3—Add ATX12V power connector information to Table 3 Section 3.3.2—Replace existing text with new text that includes the 12V requirement for processor voltage regulators Section 3.4—Moved text in Section 3.4 under a new subheading, 3.4.1. Added subheading, 3.4.2, to specify secondary side height constraints. Revised Figure 7 to reflect an increase in the maximum component height restriction. Zones C, D, and E formerly specified three different height restrictions. This revision replaces those three zones (C, D, and E) with one maximum component height restriction zone (C) for the entire region. Added two sentences at the end of the note that follows Figure 7. Section 4—Replace existing text with new text that adds the 12V connector and a reference to the ATX/ATX12V Power Supply Design Guide Section 4.2—Add references to the ATX12V connector; substitute revised Figure 10 Section 4.4—Add new Table 10 that lists wire color code for ATX12V power supplies Section 6—Update Web site URL for ATX information and document downloading Changes from Version 2.02 to Version 2.03 Replaced seven occurrences of the erroneous name “microATX” with the correct name “Mini-ATX.” The error was introduced accidentally in Version 2.02. The Mini-ATX form factor is 11.2" x 8.2" (284mm x 208mm; the Mini-ATX form factor referred to in this ATX Specification is NOT the same as the microATX form factor, which is described in a separate specification. Changes from Version 2.01 to Version 2.02 Section 3.3.5—Replaced Figures 4 and 5. Section 4.2.1—Added new section to define Aux Power Connector; renumbered the subsequent sections, figures, and tables accordingly. Section 4.2.2.3—Replaced Figure 11 to better explain the power supply timing. Section 4.2.3—Corrected two values in Table 7, Voltage Tolerances: -5VDC and -12VDC should comply to ± 10%, not ±5%. This change was made to match the newly released Intel ATX Power Supply Design Guide, Version 0.9. Section 4.4—Corrected Table 9; the 1394R signal is carried on Pin 4, and Pin 6 is Reserved. This matches the information shown in Figure 12. Section 6—Added section to provide the Internet location of the ATX home page, for access to documents with information beyond the requirements of this ATX Specification. Changes from Version 2.0 to Version 2.01 Section 2—Updated Figure 1 to reflect recommendations implemented with Version 2.0. Section 3.2—Modified Figure 2 to clarify motherboard mount requirements. Section 3.3—Updated table of requirements to reflect changes in the section outlined below. Section 3.3.5—Rewrote text to clarify requirements. Continued ATX Specification - Version 2.1 Page 4 Section 3.3.5—Reduced keepout zone requirement to 0.1" (2.5 mm). This change was based on feedback from chassis manufacturers and is the most significant requirement change with respect to the chassis. Section 3.3.5—Added recommendation to avoid paint within the keepout zone. Section 3.3.5—Replaced Figure 4 to clarify chassis I/O aperture requirements. Tolerances were added to dimensions. Section 3.3.5—Changed Figure 5 to define connector placement limitations on the motherboard. This is a new recommendation for motherboard designers to ensure clearance between the chassis and motherboard connectors for the I/O shield. Section 3.3.5—Modified Figure 6 to remove redundant dimensions, and removed Figure 7 completely. Section 4.3.2—Completely redefined FanC signal description, and removed Figure 15 completely. Minor edits were made throughout the document to improve readability and to correct minor typographical or grammatical errors. Changes from Version 1.1 to Version 2.0 Section 3.2—Changed the optional mounting hole to a required hole in chassis implementations. Changed a previously required mounting hole to “not needed.” Section 3.3.5—Added information and drawing to clarify I/O aperture requirements. Added corner radius information to the specification for clarity Section 3.4—Changed height restrictions to facilitate future processor and onboard technologies. Section 4—Added an explanation of the intent regarding the direction of air travel for cooling. Removed the external fan shown on the drawing of a suggested ATX power supply. Added a caution about external power supply fans. Added comments and drawings for duct mounting. Section 4.2—Added explanations for PS_ON#, PWR_OK, 5VSB power supply lines. The 3.3VDC power rail and soft-power control signals are being changed to required. Section 4.3—Added optional power connector for fan control, fan monitor, IEEE-1394 voltages, and remote 3.3 volt sensing. Section 4.4—Added a section to give a suggested color coding for power supply wiring. Section 4.5—Added a section suggesting a venting solution for power supplies. Section 5—Added chassis considerations. Added tables throughout the specification for clarification and easy reference of recommended and required features. ATX Specification - Version 2.1 Page 5 Contents 1. Executive Summary ......................................................................................................7 2. ATX Form-factor Overview ...........................................................................................8 3. Layout ............................................................................................................................9 3.1 Board Size.......................................................................................................................................... 9 3.2 Mounting Hole Placement .................................................................................................................. 9 3.3 Connector Placement ........................................................................................................................ 11 3.3.1 Expansion slots ..................................................................................................................... 11 3.3.2 Power Input ........................................................................................................................... 13 3.3.3 Disk I/O ................................................................................................................................. 13 3.3.4 Front Panel I/O...................................................................................................................... 13 3.3.5 Back Panel I/O ...................................................................................................................... 13 3.3.6 Memory Sockets ................................................................................................................... 16 3.3.7 Processor.............................................................................................................................. 16 3.4 Height Constraints.............................................................................................................................. 16 3.4.1 Primary (Component) Side Height Constraints..................................................................... 16 3.4.2 Secondary (Bottom/Solder) Side Height Constraints ............................................................ 18 4. Power Delivery ..............................................................................................................19 4.1 Power Supply Connectors.................................................................................................................. 19 4.1.1 Aux Power Connector for 250 W and 300 W Configurations ............................................... 20 4.1.2 2x2 Connector....................................................................................................................... 20 4.1.3 Power Signal Control Definitions........................................................................................... 20 4.1.4 Voltage Tolerances ............................................................................................................... 21 4.2 Optional Power Connector ................................................................................................................. 21 4.2.1 FanM Signal .......................................................................................................................... 22 4.2.2 FanC Signal .......................................................................................................................... 22 4.2.3 3.3 V Sense Line................................................................................................................... 23 4.2.4 1394 V Pin............................................................................................................................. 23 4.2.5 1394R Pin ............................................................................................................................. 23 5. Other ATX Chassis Considerations.............................................................................24 5.1 Venting ............................................................................................................................................... 24 5.2 Power Supply Mounting ..................................................................................................................... 24 6. Additional Information..................................................................................................24 ATX Specification - Version 2.1 Page 6 Figures Figure 1. Summary of ATX Chassis Features ............................................................................................ 8 Figure 2. ATX and microATX Form Factor Mounting Holes ....................................................................... 10 Figure 3. Sample ATX Layout Diagram ...................................................................................................... 12 Figure 4. Chassis Back Panel I/O Aperture Requirements......................................................................... 14 Figure 5. Motherboard I/O Connector Zone Recommendation .................................................................. 15 Figure 6. Example Multimedia I/O Back Panel ........................................................................................... 15 Figure 7. ATX Motherboard Maximum Component Height Restrictions..................................................... 17 Figure 10. ATX Power Supply Connector Configuration............................................................................. 19 Figure 9: 2x2 Connector Configuration ....................................................................................................... 20 Figure 12. Optional Power Supply Connector Configuration ...................................................................... 22 Figure 13. Simple Implementation of a Fan Monitor Circuit........................................................................ 22 Tables Table 1. ATX Feature Summary ................................................................................................................. 7 Table 2. Motherboard Mounting Hole Locations ......................................................................................... 9 Table 3. Connector Locations ..................................................................................................................... 11 Table 4. Height Constraints ........................................................................................................................ 16 Table 5. Aux Power Connector for High 3.3V or 5V Current Configurations .............................................. 20 Table 6. Voltage Tolerances ....................................................................................................................... 21 ATX Specification - Version 2.1 Page 7 1. Executive Summary ATX was developed as an evolution of the Baby-AT form factor and was defined to address four major areas of improvement: enhanced ease-of-use, better support for current and future I/O, better support for current and future processor technology, and reduced total system cost. ATX combines the best functionality from the form factors that dominated the computer industry in the early 1990s: the high integration of LPX and the expandability of Baby-AT. The ATX form factor is essentially a Baby AT motherboard rotated 90 degrees within the chassis enclosure and providing a new mounting configuration for the power supply. The processor is relocated away from the expansion slots, allowing them all to hold full length add-in cards. The longer side of the board is used to host more on- board I/O. Table 1 summarizes the ATX features. A change to the system form factor is ultimately of little benefit if it does not reduce overall system cost. ATX has achieved cost reduction in a number of ways: • Material cost of cables and add-in cards is reduced because more I/O can be integrated down onto the board and because the hard drive and floppy connectors can be better positioned, allowing the use of shorter cables. • Another benefit of integrated I/O down is the potential for lower EMI emissions with the removal of serial and parallel cables that can act like antennas. • Manufacturing time and inventory holding costs are reduced because the number of cables in the system is reduced. • Video-playback enhanced graphics and audio, the main hardware building blocks to support multimedia, are becoming a standard on many PCs; at the entry level, these features are quickly becoming a commodity. To reduce cost in a highly dollar-sensitive market segment, it makes sense to migrate these features down to the motherboard itself. The ATX specification is written as an open specification for the industry, designed to add value to PC architecture. Table 1. ATX Feature Summary Feature Benefit Double height flexible I/O panel allows higher integration Lower system cost Fewer cables Improved reliability Shorter assembly time Support for connectivity and I/O standards like USB, TV in/out, ISDN, etc. Integrated graphics allows use of unified frame buffer architecture Relocated drive I/O means shorter cables Reduced cost Support for faster drives such as PIO Mode 4/5 IDE drives Relocated processor and memory All full-length expansion slots Ease of use, upgrading the processor Ease of use, upgrading memory Ease of use, adding cards Relocated processor allows easier use of bulk capacitance and voltage regulation circuitry ATX Specification - Version 2.1 Page 8 2. ATX Form-factor Overview The ATX form factor allows for processor relocation away from the expansion slots, allowing the longer side of the board to be used to host more on-board I/O. For processor voltage regulators that have been designed for 12V input, an additional 12V power connector must be added. ATX power supplies with the required 12V current and associated connector are designated "ATX12V". The ATX12V mating connector is shown in Figure 10. Details on the power supply can be found in the ATX/ATX12V Power Supply Design Guide (see Section 6 for URL from which the document can be downloaded). PSU (With fan)Full Length Card Slots Floppy/IDE connectors close to peripheral bays Single power connector Easy to access memory modules CPU located near power supply 5.25” Bay3.5” Bay CPU Double High Expandable I/O System fan 12 V Connector next to Voltage Regulator Figure 1. Summary of ATX Chassis Features ATX Specification - Version 2.1 Page 9 3. Layout The following sections describe the mechanical specification of the ATX form factor motherboard, including physical size, mounting hole placement, connector placement, and component height constraints. 3.1 Board Size A full size ATX board is 12" wide by 9.6" deep (305mm x 244mm). This allows many ATX form factor chassis to accept microATX boards as well. 3.2 Mounting Hole Placement Table 2. Motherboard Mounting Hole Locations Feature Status Comment Motherboard mounting hole locations Required See Figure 2 for an overview and Figure 3 for exact locations. All ATX board mounting locations shown should be implemented for full ATX 2.1 compliance. Where possible, the ATX mounting holes line up with mounting holes used for microATX boards. Three holes have been defined to provide mechanical support along the front edge of the full size ATX board. • Figure 2 shows the relative outlines of the ATX and microATX boards. This figure uses letter callouts to show the general location of the mounting holes for the ATX and microATX form factors. The accompanying table indicates which holes are required for each form factor. • Figure 3 shows the exact location (dimensions) of the mounting holes for ATX boards. Must be used All ATX board mounting locations listed in the table in Figure 2 should be implemented for chassis assemblies to achieve full ATX 2.1 compliance and to provide proper support for the board in these areas. The hole at F in Figure 2 (upper right corner of the ATX board) must be implemented in all ATX 2.1- compliant chassis assemblies to accommodate boards requiring this mounting hole. This hole was labeled optional in